Answer:
12
Step-by-step explanation:
Let d represent the number of dimes Lily saved. Then the value of her coins in cents is ...
10d +100(16-d) = 520
-90d +1600 = 520 . . . . . eliminate parentheses, collect terms
-90d = -1080 . . . . . . . . . . subtract 1600
d = -1080/-90 = 12 . . . . . divide by the coefficient of d
Lily has 12 ten-cent coins.
